. >>> at an appearance in las vegas, president obama said the united states will be relentless in tracking down the militants responsible for the attack on the consulate. he is vowing that they will be brought to justice. ken wayne is here now with one working theory about the motive, and how the u.s. is responding. >> two navy destroyers have been deployed to the coast of libya. it arrived today. amend the uss mcfall, coming from the strait of gibralter. the missiles travel about 550 miles per hour, and are equipped with gps for pinpoint accuracy. it is just one of the moves the united states has made in response to the killings of benghazi. >> reporter: earlier, he vowed those responsible will be found. >> we will not waiver in our commitment to see that justice is done for this terrible act. and make no mistake, justice will be done. >> how could this be done in a country we helped liberate, in a city we helped save from destruction? this question reflects just how complicated and at times, how confounding the world can be. >> we are very sorry for what happened. we will do everything p